Capacitors include a solid electrolytic capacitor having a low equivalent series resistance (ESR), and an aluminum electrolytic capacitor having a high withstand voltage. The solid electrolytic capacitor is used around the central processing unit (CPU) of a personal computer. The aluminum electrolytic capacitor is used for the inverter power supply for a large machine, and the inverter power supply for an automobile, such as a hybrid vehicle. There is a strong demand that these capacitors have smaller sizes and larger capacities.
In a conventional solid electrolytic capacitor, for example, an electrode-foil is used as the positive electrode. The electrode-foil includes a foil whose surface is roughened by etching or vapor deposition, and a dielectric film of an oxide film formed on the surface of the foil (see Patent Literature 1 and 2, for example).
In the conventional electrode-foil, the dielectric film is formed by anodizing the foil. That is, since the dielectric film is made of an oxide of a metal constituting the foil, the dielectric constant and withstand voltage are affected by the materials of the foil. Thus, the conventional electrode-foil has a low degree of flexibility in increasing the dielectric constant or reducing the film thickness. This poses a limitation on the increase in the capacity of the capacitor.